NFC is a technique increasingly used mainly in Asian areas in the fields of traffic systems, accounting, and certification, for example. This technique has been approved as an international standard. The specification for the NFC, which is also referred to below as the NFC specification, has compatibility, i.e., so-called upward compatibility, for example, with various other specifications, such as Type A, Type B, FeliCa (registered trademark), and IS015693 specifications. In other words, when a reader-writer or a card is compatible with the NFC specification, it is also compatible with all of those specifications.
In the NFC, as an example, a reader-writer subjects data to an amplitude shift keying (ASK) modulation and then transmits this data to a card. In turn, the card subjects data to a load modulation and then transmits this data to the reader-writer. PTLs 1 and 2 disclose examples of a communication device that is able to conduct communication using a load modulation, specifically, a passive load modulation.
On the other hand, some electronic circuits use phase locked loop (PLL) circuits, as disclosed in PTL 3, for example.